Pivot Joint:
A pivot joint is a type of synovial joint that allows rotational movement between two bones. It is also known as a rotary joint. In a pivot joint, one bone rotates around a peg-like process of another bone. This type of joint is found in various parts of the body, such as the neck, where it allows rotational movement of the head.

Explanation:
A pivot joint is characterized by a cylindrical or peg-like process of one bone that fits into a ring or notch of another bone. The cylindrical process acts as a pivot point, allowing the bone to rotate around it. This type of joint provides rotational movement without allowing any other types of movement such as flexion or extension.

For example, the pivot joint between the first and second vertebrae of the neck, known as the atlantoaxial joint, allows the head to rotate from side to side. The first vertebra, known as the atlas, has a ring-like structure with a peg-like process called the dens or odontoid process. This dens fits into the ring-like structure of the second vertebra, known as the axis. This arrangement allows the head to rotate freely.

Pivot joints are also found in the forearm, where the radius bone rotates around the ulna bone. The head of the radius has a rounded shape that fits into a shallow socket on the ulna. This allows for the rotation of the forearm, such as when turning a doorknob or rotating the palm upward or downward.

Overall, a pivot joint is a type of synovial joint that allows for rotational movement between two bones. It is characterized by a cylindrical or peg-like process of one bone fitting into a ring or notch of another bone. This joint is important for rotational movements in various parts of the body, such as the neck and forearm.